1. Field of the Invention
The present invention relates to a power factor correction circuit and a power supply apparatus thereof. More particularly, the present invention relates to a power factor correction circuit and a power supply apparatus thereof, which may reduce an electromagnetic interference (EMI).
2. Description of Related Art
In evaluation criteria for various electronic apparatuses, electromagnetic compatibility (EMC) thereof is an essential quality indicator. Evaluation of the EMC includes electromagnetic interference (EMI) and electromagnetic susceptibility (EMS). Since signal transmission speed of a present electronic apparatus is increasingly fast, the EMI caused by electronic components within the electronic apparatus becomes more and more serious, so that normal operations of other electronic components within the electronic apparatus are influenced.
Generally, the EMI is mainly transmitted into a circuit via a power supply. Therefore, in a server, to match with some corresponding standards, an EMI test is also a key test for the power supply. Moreover, the present power supply generally has at least one switch device, and voltages to be output may be generated by turning on/off the switch device.
However, with repeated switching of the switch device, the EMI caused by the power supply is increased. Though the present power supply may constantly adjust a frequency of an internal pulse width modulation (PWM) signal thereof to mitigate the EMI, how to adjust the frequency of the PWM signal while maintaining a stable power output is still an issue under development.